No, the images don't have to be from imgur! As long as they have extensions at the end of the link you're trying to copy/paste (.jpg, .png, etc.), you'll be fine.

As for putting personal images from an iPad to PMC without imgur (or any site like it), you really can't. Unless you're allowed to use imgrpost, which is a site where you can make your photos private to others if you want, then good luck my friend because that's impossible without an actual website link (Sites use www while personal files have a format like this when you try opening it with a browser, PC or otherwise: users/someguy/somedesktop/somefolder/somefile)... :P